This invention relates to a new and improved thread convolution. More specifically, the invention relates to a lock thread convolution having a resiliently deflectable spring rib or projection which cooperates with a mating thread to provide a locking action which retards relative rotation between the lock thread convolution and the mating thread.
It has been proposed that a locking action could be obtained between a lock thread convolution and a mating thread by providing burrs or points which extend from the crest of the lock thread convolution. These burrs engage the flank of a mating thread to prevent relative rotation between the threads. The burrs are sharply pointed and extend transversely to the flank of the mating thread so that the burrs gouge or cut into the mating thread. The manner in which such a thread convolution may be formed is disclosed in U.S. Pat. No. 3,076,208. Due to a lack of flexibility in the burrs and resulting damage to a mating thread, the lock thread convolution disclosed in this patent has limited reusability.
Another known lock thread is provided with a pair of tangs or projections which extend outwardly from opposite flanks of the lock thread. These tangs or projections cooperate with the flanks of a mating thread to center the lock thread convolution midway between the flanks of the mating thread. When a load is applied to the thread convolutions, the tangs on the load or pressure flank side of the lock thread convolution are compressed while the tangs on the opposite side of the lock thread tend to move away from the cooperating flank of the mating thread. The tangs are formed by sharply cutting into the body of the lock thread in such a manner as to induce sharp stress concentrating discontinuities in the body of the lock thread. The manner in which this known lock thread is formed and cooperates with an internal thread is disclosed in U.S. Pat. No. Re. 27,678. Due to the relatively thin configuration of the tangs, it is difficult to manufacture this lock thread with commercially acceptable tooling.